At 10.31 hours on 15 Jan 1943, U-617 fired four torpedoes at a small convoy, consisting of two merchants, the Annitsa and Harboe Jensen, escorted by the British armed trawler HMS Southern Isles. Brandi observed two hits on each merchant, that had a great effect. Both merchants were sunk in the attack.

The Harboe Jensen (Master Sverre Aanonsen) was hit by two torpedoes on the port side, broke in two and sank immediately. The master, 15 crew members and two gunners were lost. Five crew members and one gunner jumped overboard and found an upturned lifeboat which they righted. They picked up two survivors from the Greek ship, before they were rescued by the trawler. Gunner Falkensten, who had also jumped overboard kept himself afloat on a plank and was also rescued by the escort after about an hour. All survivors were landed at Tobruk on 16 January.